1. Field of the Invention
The present invention relates to a filter provided at a fuel intake of a piston type high-pressure fuel pump and, more particularly, to a filter for a piston type high-pressure fuel pump which does not clog up from freezing.
2. Description of the Related Art
Diesel engines have been widely known as the type of internal-combustion engines called "cylinder injection internal-combustion engines" or "direct injection internal-combustion engines" wherein fuel is injected in engine cylinders. In recent years, the cylinder injection type has been proposed also for spark ignition engines or gasoline engines. There is a tendency in such a cylinder injection internal-combustion engine to increase fuel injection pressure to produce particulate fuel spray to shorten the fuel injection period in order to achieve higher performance of the engine and to reduce emission gas. An engine provided with a supercharger requires a high fuel injection pressure to match charging pressure at the time of supercharging. For this reason, the fuel supply system in the gasoline cylinder direct injection internal-combustion engine is adapted to provide a sufficiently high fuel injection pressure of, for example, about 10 atm.
FIG. 7 is a schematic block diagram showing a conventional fuel supply system. In FIG. 7, a delivery pipe 1 has as many injectors 1a as the cylinders of a gasoline cylinder direct injection internal-combustion engine, which is not shown. A high-pressure fuel pump 100 is disposed between the delivery pipe 1 and a fuel tank 2, the delivery pipe 1 and the high-pressure fuel pump 100 being connected by a high-pressure fuel pipe 3. The high-pressure fuel pump 100 and the fuel tank 2 are connected by a low-pressure fuel pipe 4 serving as a fuel intake route. The low-pressure fuel pipe 4 located upstream from the high-pressure fuel pump 100 is provided with a filter 5. A drain 6 of the high-pressure fuel pump 100 is routed back to the fuel tank 2.
The low-pressure fuel pipe 4 is provided with an in-tank, low-pressure fuel pump 7 at the end thereof on the fuel tank 2 side. A filter 8 is provided at the fuel intake of the low-pressure fuel pump 7. The low-pressure fuel pipe 4 is further provided with a low-pressure regulator 10 located between the high-pressure fuel pump 100 and the low-pressure fuel pump 7. A drain 11 of the low-pressure regulator 10 is routed back to the fuel tank 2.
The delivery pipe 1 also has a high-pressure fuel passage 12 at the opposite end from the high-pressure fuel pump 100. The high-pressure fuel passage 12 is provided with a high-pressure regulator 14, a drain 21 of the high-pressure regulator 14 being routed back to the fuel tank 2.
In such a fuel supply system having the constitution described above, the fuel is pressurized to a certain degree by the low-pressure fuel pump 7 and further pressurized by the high-pressure fuel pump 100 before reaching the delivery pipe 1, then it is injected through the injector 1 a into an engine cylinder, which is not shown. At this time, the discharge pressure from the low-pressure fuel pump 7 is stabilized by the low-pressure regulator 10 such that it stays within a predetermined range, and the discharge pressure from the high-pressure fuel pump 100 is also stabilized by the high-pressure regulator 14 such that it stays within a predetermined range. The fuel supplied to the high-pressure fuel pump 100 is filtered through the filter 5 to prevent foreign matter in the fuel from entering the high-pressure fuel pump 100. A plurality of the mesh openings of the conventional filter 5 have been formed so that one side of each square mesh opening measures 30 .mu.m.
In the fuel supply system having the constitution described above, since each of the openings of the filter 5 provided at the upstream of the high-pressure fuel pump 100 is formed into a rectangle, one side of which measuring 30 .mu.m, the filter has been clogged up from time to time by frozen moisture in fuel or gasoline.